This invention relates to a burner and, more particularly, to a burner for gas turbine engines having a ring-shaped swirling device which is coaxially assigned to a fuel nozzle. The swirling device forms tangential ducts between profiled surfaces distributed along the circumference for an adjustable feeding of combustion air.
In the case of modern burners and combustion chamber designs for gas turbine engines, a combustion that is low in pollutants is endeavored, particularly in the primary zone of the combustion chamber. It was found that a significant reduction of the emission of pollutants can be achieved in the case of a comparatively low combustion temperature of &lt;1,900.degree. K. in combination with a comparatively high proportion of air with respect to the fuel fed.
In addition, relatively low pollutant emissions require, among other things, a uniform processing of the fuel-air mixture to be supplied to the primary zone as well as good combustion efficiency. This is particularly true in the case of burners known according to German Patent Document DE-PS 24 42 895 which operate with air support as "low-pressure systems" with a high fuel atomization efficiency and a partial wall-side and aerodynamic fuel evaporation. However, the known case does not provide swirling devices which can be adjusted with respect to the air flow rate in order to control different operating conditions with respect to correspondingly required variable fuel-air flow rates in a manner that is as low in pollutants as possible.
Furthermore, combustion chamber concepts which, in the interest of providing low polluting combustion, provide a "variable chamber geometry" in order to supply combustion air and possibly mixed air by way of holes of the rows of holes are high in construction expenditures, technically complex, susceptible to disturbances and expensive. These devices can be controlled in their cross-sections by pipe sections of the flame tube jacket of the combustion chamber which can be displaced relative to one another in the axial or circumferential direction.
From European Patent Document EP-PS 0251895, an annular combustion chamber for a gas turbine engine is known. In this case, in order to provide a low polluting combustion, an "external" swirling device is assigned to each burner. The swirling device can be regulated with respect to the supply of a portion of the combustion air.
In the known case, a screen which can be rotated on the outside on a central body in the circumferential direction and which has webs on openings distributed along the circumference performs the regulation. The webs, according to their length, only partly project into radial/tangential openings of the central body. The webs project in such a manner that in intermediate positions of the screen, they each have an angular position which deviates from the openings. In the intermediate positions which are decisive for performing the regulating, a guiding of the duct is obtained which throttles the air flow at the inlet, is divergent in the direction of the flow, and expands abruptly downstream of the trailing edge of the web in the direction of a large-surface duct outlet. In the process, the respective circumferential component of the flow at the respective outlet of the opening is clearly weakened via a separating diffuser flow, whereby generation of the required swirl is considerably impaired. This is a significant disadvantage with respect to developing a uniform turbulence, such turbulence being required during the whole operating condition, as well as a resulting uniform and stable low polluting combustion.
There is therefore needed a burner of the initially mentioned type, in the case of which, while the construction is relatively simple, more compact and lighter, at least one swirling device permits the air flow rate required for a combustion which is uniform and low in pollutants while a uniformly pronounced rotation whirl is formed over a large control range.
According to the present invention, these needs are met by a burner for a gas turbine engine having a ring-shaped swirling device which is coaxially assigned to a fuel nozzle and which forms, between profiles arranged along the circumference, tangential flow ducts for an adjustable feeding of combustion air. The ring-shaped swirling device comprises annular disks which are profiled on their faces with engaging claws. The cross-sections of said flow ducts are controlled by respective axial displacement of at least one of the two annular disks with the engaging claws.
The present invention provides variable swirling ducts which are each distributed uniformly along the circumference and can be constructed in a relatively simple manner. The swirling ducts, in a section view transverse to the swirling device, are always designed to be uniform, for example, wedge-shaped. In this case, the respective duct width, in the direction of the burner axis, of all the ducts, is uniformly variable along the entire length of the ducts. This is all the result of the fact that the respective profiles with their linear faces can be axially moved more or less deep into the corresponding recesses. For example, in an end position in which the profiles and the recesses are completely pushed into one another, the swirling device can be completely blocked off on the air supply side. Despite a relatively large adjusting or regulating range, a burner with such a swirling device can be manufactured in a lighter and more compact construction.
In all embodiments of the present invention, also within the scope of further developments, profiled and walled duct structures are provided. The structures are enclosed along the entire duct length. On the structures, significant dynamic disturbance factors which could impair the respective required swirling efficiency and, in turn, the rotational whirl geometry in the primary zone, do not occur either on the inlet side, the flow-through side, or on the outlet side.
Constructions of the adjustable swirling device which are possible as further embodiments of the invention permit relatively large air flow rates, while the manufacturing is economically acceptable and the construction is compact and light. The profiles have additional frontally open duct recesses which, in a completely pushed-in end position of the remaining profiles and recesses with adjacent component faces, make available the smallest cross-sections of the swirling ducts. By performing an axially opposite component adjustment to the last-mentioned end position, advantageously larger, or a largest, duct cross-section may be adjusted. These cross-sections are preferably constructed in the direction from the outer to the inner ring circumference of the swirling device, while they narrow down in the shape of a wedge or a nozzle. This is so that, also in the case of large amounts of air, a good swirling efficiency and thus a good rotational whirl development is achieved.
Using the adjustable swirling device, all or a significant portion of the primary air which is required for a combustion that is low in pollutants can be supplied. The swirling device can be adjusted for the flow rate of relatively small and relatively large amounts of air.
In an advantageous further embodiment, the present invention permits the combination of at least one controllable or adjustable swirling device with a stationary swirling device. This makes available a constant air supply during the whole operating condition. The fuel supply is varied depending on the load condition, in which case an air supply is "superimposed" on the variable operating conditions which, while being adapted to the respective operating conditions, meets the air requirement with respect to a low polluting combustion. The latter air requirement may be regulated, for example, as a function of an operationally increasing combustion temperature and/or pressure in the combustion chamber. The present invention includes the possibility of burning, for example, stoichiometrically, in certain engine conditions, as well as dependent on the design and use spectrum of the engine, i.e., during the ignition and start of the operation, as well as possibly during an extreme full load, and to burn, predominantly in the cruising operation, with a large amount of air and therefore in a manner than is low in pollutants.
The concerned swirling devices may generate rotational or mixed air swirls which rotate with respect to the burner axis or nozzle axis approximately in the same direction or in mutually opposite directions.